1. Field of the Invention
The present invention relates to a semiconductor memory device, such as a DRAM (Dynamic Random Access Memory), which needs to be refreshed for retaining data, an electronic apparatus which uses such a semiconductor memory device, and a semiconductor memory device which is suitable as a semiconductor memory device for saving data therein, for example, used in such an electronic apparatus.
2. Description of the Related Art
For example, although a DRAM has been used as a main storage memory of a personal computer, a server or the like until now, an era in which a large-capacity DRAM is used in a simple terminal such as a cellular phone is coming due to progress of Internet technology, mobile technology and so forth.
Currently, a SRAM (Static Random Access Memory) is mounted in a simple terminal such as a cellular phone. However, when a DRAM is used instead of a SRAM, or a DRAM and a SRAM are used together, it is necessary to consider that the DRAM needs to be refreshed for retaining data, different from the SRAM.
Therefore, it is required that, first, a DRAM mounted in a simple terminal such as a cellular phone be such that control of the DRAM by a controller can be easily performed, and, second, a simple terminal such as a cellular phone is such that, when a main battery goes dead, or is removed, and, thereby, power supply by the main battery is stopped, power consumption of a backup battery due to refresh of the DRAM can be reduced as much as possible.
The present invention has been devised in consideration of the above-mentioned point, and a first object of the present invention is to provide a semiconductor memory device performing a refresh operation for retaining data, and control of which by a controller is easy. A second object of the present invention is to provide an electronic apparatus which is provided with a semiconductor memory device performing a refresh operation for retaining data and a controller, and, in which control of the semiconductor memory device by the controller is easy. A third object of the present invention is to provide a semiconductor memory device such that saving of data, from another semiconductor memory device, in the semiconductor memory device can be easily performed. A fourth object of the present invention is to provide a semiconductor memory device such that saving of data from the semiconductor memory device is easy.
A semiconductor memory device according to a first aspect of the present invention, performing a refresh operation for retaining data, comprises:
a memory portion for storing data therein; and
a busy signal outputting portion outputting a busy signal during the refresh operation.
When the semiconductor memory device according to the first aspect of the present invention is applied to a semiconductor memory device, which performs a refresh operation for retaining data, of an electronic apparatus including the semiconductor memory device and a controller which controls the semiconductor memory device, because the controller can recognize whether or not it is the time for the refresh operation, control of the semiconductor memory device by the controller can be easily performed.
An electronic apparatus according to a second aspect of the present invention comprises:
a semiconductor memory device which performs a refresh operation for retaining data and outputs a busy signal during the refresh operation; and
a controller controlling the semiconductor memory device and being able to receive the busy signal.
When the second aspect of the present invention is applied to an electronic apparatus which includes a semiconductor memory device which performs a refresh operation for retaining data and a controller controlling the semiconductor memory device, because the controller can recognize whether or not it is the time for the refresh operation of the semiconductor memory device, control of the semiconductor memory device by the controller can be easily performed.
A semiconductor memory device according to a third aspect of the present invention comprises:
an automatic writing portion which, when automatic writing is externally instructed to be performed, automatically writes data to the device in internally generated addresses; and
an automatic writing indicating signal outputting portion which outputs an automatic writing indicating signal, which indicates that automatic writing is being performed, during the automatic writing operation.
According to the third aspect of the present invention, because the automatic writing portion which, when automatic writing is externally instructed to be performed, automatically writes data to the device in internally generated addresses is provided with, saving of the data of a first semiconductor memory device can be easily performed when an electronic apparatus including the first semiconductor memory device and a controller for controlling the first semiconductor memory device is provided with a second semiconductor memory device for saving therein the data stored in the first semiconductor memory device and the third aspect of the present invention is used as the second semiconductor memory device, for example.
A semiconductor memory device according to a fourth aspect of the present invention, comprises an automatic reading portion which comprises:
an address counter which generates an address for automatically reading data from the device when automatic reading is externally instructed to be performed; and
an access-accepting allowing/rejecting signal receiving portion which receives an access-accepting allowing/rejecting signal output from a data transfer destination and indicating whether or not the destination agrees to accept access,
wherein the automatic reading portion automatically reads data from the device when automatic reading is externally instructed to be performed and the access-accepting allowing/rejecting signal indicates that the destination agrees to accept access.
According to the fourth aspect of the present invention, because the automatic reading portion which automatically reads data from the device when automatic reading is externally instructed to be performed and the access-accepting allowing/rejecting signal indicates that the data transfer destination agrees to accept access is provided with, it is possible to easily transfer data to (save data in) the data transfer destination (data saving destination), which outputs the access-accepting allowing/rejecting signal, when it is necessary to transfer the data (it is necessary to save the data, for example).
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.